Sustained or extended release dosage forms which comprise a single active component are well known. A matrix tablet system incorporates active ingredients, lubricants, binders, fillers and other excipients, wherein the binders may be hydrophilic, hydrophobic or water insoluble polymers. See for example U.S. Pat. No. 4,389,393.
The mechanism by which sustained release dosage forms act to dispense the active ingredients over a period of time have been described at length in the literature. See for example Manford Robinson, Chapter 14, "Sustained Action Dosage Forms," The Theory and Practice of Industrial Pharmacy, 2nd, ed., ed. L. Lachman, H. Lieberman and J. Kanig (Philadelphia; Lea & Febiger, 1976).
Sustained release dosage forms which combine two or more actives are not common, because of the difficulties encountered in combining multiple actives, each with different chemical and physical characteristics, different release rates, different half-lives and different dosage sizes. However, three U.S. Patents do exist which are directed to the sustained release of two or more actives.
U.S. Pat. Nos. 4,601,894, 4,657,757 and 4,695,591 describe controlled-release dosage forms which incorporate acetaminophen, pseudoephedrine sulfate and dextrobrompheniramine maleate with a polymeric material. Both U.S. Pat. Nos. 4,601,489 and 4,687,757 describe a controlled release system which contains hydroxypropyl methyl cellulose (HPMC) and a second polymer selected from the group consisting of ethyl cellulose, methyl cellulose, sodium carboxymethyl cellulose or other cellulose ethers. U.S. Pat. No. 4,695,591 describes a one component controlled release system containing only HPMC U.S.P. 2910.
However, none of these patents recognize that a superior controlled release dosage form can be obtained by incorporating one or more pharmaceutical actives in a polymeric matrix of hydroxypropyl cellulose (HPC) and hydroxyethyl cellulose (HEC).